Ozone-Generating Air Cleaners and Indoor Air
Chemistry
Ozone-generating air cleaners are marketed to homeowners as well as business establishments ostensibly to remove odors and other contaminants from indoor air. IEMB has characterized ozone and oxides of nitrogen (NOx) emissions from these devices in full-scale environmental chamber tests and characterized performance in a research test house. To date, findings demonstrate that, for those models tested, ozone generation rates are generally within the ranges stated by the manufacturers and some models have the capacity to generate ozone concentrations of 200 parts per billion (ppb) in the test house, well above EPA’s 8-hour ambient ozone standard of 80 ppb. Additionally, ozone and nitrogen dioxide emission rates increase with decreasing relative humidity, and the relationship between ozone emission rate and NOx generation rate varies between different models of different manufacturers. Ozone-generating air cleaners equipped with an ozone sensor/controller designed to prevent activation of the ozone generator at concentrations above 50 ppb performed erratically in full-scale chamber tests but appeared to perform as designed in limited short-term (24 h) tests in a research test house. We conclude that more extensive testing is needed to characterize the sensor/controller. However, tests in the research test house clearly demonstrate that these devices are capable of producing ozone concentrations well above those of accepted health guidelines.
IEMB is currently investigating the impact of ozone generators on concentrations of volatile organic compounds (VOCs) in indoor environments. These experiments investigate the chemical reactions that take place when an ozone-generating air cleaner is operated in the presence of emissions from a typical source of VOCs, such as an air freshener or cleaning product. Results demonstrate that the ozone-generating air cleaners have little impact on airborne concentrations of solvents used in consumer products, but do impact concentrations of many of the fragrance compounds emitted by this type of product. Reaction products include formaldehyde and other oxygenated organics. The interaction between ozone and some of the product emissions, such as terpenes, triggers formation of ultrafine particles. IEMB is currently refining analytical approaches to better characterize the “soup” of particles and gases that results from operation of these devices in the presence of VOCs.
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According to the EPA’s website the same chemical properties that allow high concentrations of ozone to react with organic material outside the body give it the ability to react with similar organic material that makes up the body, and potentially cause harmful health consequences. When inhaled, ozone can damage the lungs (see – “Ozone and Your Health” – www.epa.gov/airnow/brochure.html). Relatively low amounts can cause chest pain, coughing, shortness of breath, and, throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections. People vary widely in their susceptibility to ozone. Healthy people, as well as those with respiratory difficulty, can experience breathing problems when exposed to ozone. Exercise during exposure to ozone causes a greater amount of ozone to be inhaled, and increases the risk of harmful respiratory effects. Recovery from the harmful effects can occur following short-term exposure to low levels of ozone, but health effects may become more damaging and recovery less certain at higher levels or from longer exposures (US EPA, 1996a, 1996b).